From U.S. Pat. No. 3,487,187 and 3,435,171, for example, and others, it is known to wind a synthetic yarn in one or more turns about the rotary drum of a heated godet to heat the yarn for stretching or some other modification of the yarn structure. Such devices are widely used in plants for the production of synthetic yarn between the spinerettes in which the synthetic filaments are produced, and the machine parts at which the synthetic yarn is wound in bobbins or in yarn packages. Control of the temperature is described, for example, in the commonly owned copending application Ser. No. 08/630,823 of 10 Apr. 1996 (now U.S. Pat. No. 5,712,467 of 27 Jan. 1998).
Godets for the aforedescribed purpose can be heated by means of liquid or gaseous media and, for example, superheated steam or a medium which condenses in the heating process. Heating can also be effected by electrical resistance heaters. Perhaps the best results to date are obtained by heating the godets utilizing induction heating techniques with, for example, a primary winding of the induction heater located within the interior of the godet and fed with alternating current to induce, in a magnetostrictive material like steel or copper forming the shell of the godet, eddy currents which, in turn, generate heat.
In DE 43 13 837, moreover, different zones of the godet are differently heated or supplied in a controlled manner with the different amounts of energy to satisfy the desire for heating the yarn differently in these zones.
The cost of heating godets of this type are considerable, especially with godets of large diameters up to, say 300 mm, and considerable lengths of say 500 mm or more. These costs include the high capital cost as well as the high energy cost, the latter being a consequence in part of the high energy losses in such systems.